Due to the increase of meat prices, the warm water aquaculture of fresh water prawns or shrimp has become an increasingly active industry for providing a protein food source at reasonable prices.
The three main processors involved in the aquaculture of fresh water shrimp include hatching, larval rearing and the grow-out process. The grow-out process accounts for 95% of the total cost of the cultivation of the shrimp, the two main sources of expense in the grow-out process being harvesting cost and the mortality of the shrimp. Heretofore, the harvesting of the shrimp was accomplished manually by hand nets, a time-consuming process requiring many man hours resulting in large labor costs. The mortality of the shrimp is caused by the resultant injury to the shrimp during the manual harvesting and by the larger shrimp eating the smaller or less developed shrimp.
In order to reduce the cost of the grow-out process, after considerable research and experimentation, the harvester of the present invention has been devised which comprises, essentially, an inclined ramp, having a slot formed therein, extending between adjacent tanks of water. Water is caused to flow down the ramp, whereby the shrimp move upstream thereon, based on the principle of rheotactic response; that is, the tendency for shrimp to naturally travel upstream. The smaller shrimp pass through the slot in the ramp and return to the original tank while the larger shrimp go over the slot and into the next tank. By this construction and arrangement, the shrimp are segregated or sorted by size, the smaller shrimp being in the original tank and the larger shrimp being in the next adjacent tank. By providing a series of tanks having inclined ramps extending between adjacent tanks in the series and with each ramp having a progressively larger slot than the previous ramp in the series, the sorting of the shrimp can be accomplished whereby the smallest shrimp are contained in the first tank and the largest shrimp are contained in the last tank in the series, while the various sized shrimp are contained in the respective tanks between the first and last.